Fossil range: Cambrian or earlier – Recent
Tarantula Brachypelma sp. The Cambrian is a geologic period and system that began about Ma (million years ago at the end of the Proterozoic eon and ended about Ma with
|Subphyla and Classes|
Arthropods are animals belonging to the Phylum Arthropoda (from Greek ἄρθρον arthron, "joint", and ποδός podos"foot", which together mean "jointed feet") and include the insects, arachnids, crustaceans and allies. Greek (el ελληνική γλώσσα or simply el ελληνικά — "Hellenic" is an Indo-European language, spoken today by 15-22 million people mainly A joint is the location at which two or more Bones make contact The foot is an Anatomical structure found in many Animals It is the terminal portion of a limb which bears weight and allows Locomotion. Insects ( Class Insecta) are a major group of Arthropods and the most diverse group of Animals on the Earth with over a million described Arachnids are a class ( Arachnida) of joint-legged Invertebrate Animals in the subphylum Chelicerata. Structure of crustaceans As Arthropods crustaceans have a stiff Exoskeleton, which must be shed to allow the animal to grow ( Ecdysis or molting Arthropods are characterized by the possession of a segmented body with appendages on at least one segment. Segmentation in biology refers to the division of some Metazoan bodies and Plant body plans into a series of semi-repetitive segments and the question of An appendage in the broadest sense is an additional or subsidiary part existing on or added to something which can generally still function if the appendage has never existed or They have a dorsal heart and a ventral nervous system. In Anatomy, the dorsum is the upper side of animals that typically run fly or swim in a horizontal position and the back side of animals (like humans that walk upright The heart is a muscular organ in all Vertebrates responsible for pumping Blood through the Blood vessels by repeated rhythmic The ventral nerve cords make up the Nervous system of some phyla of the Invertebrates particularly within the Nematodes Annelids and All arthropods are covered by a hard exoskeleton made of chitin, a polysaccharide, which provides physical protection and resistance to desiccation. An exoskeleton is an external Skeleton that supports and protects an animal's body in contrast to the internal Endoskeleton of for example a Human. Chitin ( C 8 H 13 O 5 N)n (ˈkaɪtən is a long-chain Polymer of a N-acetylglucosamine Polysaccharides are relatively complex Carbohydrates They are Polymers made up of many Monosaccharides joined together by Glycosidic bonds Desiccation is the state of extreme dryness or the process of extreme drying Arthropods grow by shedding this covering in what are termed molts. In Biology, moulting (or molting, also known as shedding or for some species Ecdysis) signifies the manner in which an animal routinely
They are the largest phylum in the Animal Kingdom with more than a million described species making up more than 80% of all described living species, and a fossil record reaching back to the late proterozoic era. FOSSIL is a standard protocol for allowing serial communication for Telecommunications programs under the DOS Operating system. The Proterozoic (ˌproʊtərəˈzoʊɪk is a geological eon representing a period before the first abundant complex life on Earth. Arthropods are common throughout marine, freshwater, terrestrial, and even aerial environments, as well as including various symbiotic and parasitic forms. This article is about the biological phenomenon for other uses see Symbiosis (disambiguation The term symbiosis (from the Greek Parasitism is a type of symbiotic relationship between Organisms of different Species. They range in size from microscopic plankton (~¼ mm) up to forms several metres long. Plankton consist of any drifting Organisms ( Animals Plants Archaea, or Bacteria) that inhabit the Pelagic zone of The Millimetre ( American spelling: millimeter, symbol mm) is a unit of Length in the Metric system, equal to The metre or meter is a unit of Length. It is the basic unit of Length in the Metric system and in the International The largest living arthropod is the Japanese spider crab, with a leg span up to 3½ m (12 ft), and some prehistoric arthropods were even larger, such as Jaekelopterus and Arthropleura. The Japanese spider crab, Macrocheira kaempferi, is the largest known Arthropod; fully grown it can reach a leg span of almost 4  m (13  The metre or meter is a unit of Length. It is the basic unit of Length in the Metric system and in the International A foot (plural feet or foot; symbol or abbreviation ft or sometimes &prime – the prime symbol) is a non-SI unit Jaekelopterus rhenaniae (" Otto Jaekel 's wing from the Rhineland " is an extinct species of the Eurypterida (sea scorpions Arthropleura was a 03–26  Metre (1–85  feet) long relative of Centipedes and Millipedes native to the Upper
The success of arthropods is related to their hard exoskeleton, segmentation, and jointed appendages. The blue crab ( Callinectes sapidus, from the Greek calli ="beautiful" nectes ="swimmer" and Latin An exoskeleton is an external Skeleton that supports and protects an animal's body in contrast to the internal Endoskeleton of for example a Human. An appendage in the broadest sense is an additional or subsidiary part existing on or added to something which can generally still function if the appendage has never existed or The appendages are used for feeding, sensory reception, defense, and locomotion. The muscle system is more or less assisted by hydraulics originated from the blood pressure, created by the hearts of the animals.  The hydraulic system in spiders is especially well developed.
Aquatic arthropods use gills to exchange gases. Harpaphe haydeniana (the yellow-spotted millipede, almond-scented millipede or cyanide millipede) is a Millipede found in the The tropical diaprepes root weevil ( Diaprepes abbreviatus) was described for the first time by Carolus Linnaeus as Curculio abbreviatus An aquatic animal is an Animal which lives in water for most or all of the time A gill is an anatomical structure found in many aquatic organisms These gills have an extensive surface area in contact with the surrounding water. Surface area is the measure of how much exposed Area an object has Terrestrial arthropods have internal surfaces that are specialised for gas exchange. Terrestrial animals are Animals that live predominantly or entirely on land as compared with Aquatic animals which live predominantly or entirely in the water (e Gas exchange or respiration takes place at a respiratory surface—a boundary between the external environment and the interior of the body Insects and most other terrestrial species have tracheal systems: air sacs leading into the body from pores called spiracles in the epidermis cuticle. Many terrestrial Arthropods have evolved a closed Respiratory system composed of Spiracles, tracheae and Tracheoles to transport metabolic Spiracles are small openings on the surface of some Animals that usually lead to Respiratory systems In Elasmobranchs ( Sharks and In Biology, the term cuticle or cuticula is given to a variety of tough but flexible non-mineral outer coverings of an organism or part of an organism that Others use book lungs, or gills modified for breathing air as seen in species like the coconut crab. A book lung is a type of Respiration organ used for atmospheric gas exchange and is found in Arachnids such as Scorpions and Spiders Each of these A gill is an anatomical structure found in many aquatic organisms The coconut crab ( Birgus latro) is the largest land-living Arthropod in the world Some areas of the legs of soldier crabs are covered with an oxygen absorbing membrane. The gill chambers in terrestrial crabs sometimes have two different structures: one that is gilled and used for breathing underwater, and another specially adapted to take up oxygen from the air (a pseudolung). Arthropods also have a complete digestive system with both a mouth and anus.
Arthropods have an open circulatory system. This is an article about the rock music band "Circulatory System" Haemolymph containing haemocyanin, a copper-based oxygen-carrying protein (the copper makes the blood blue, unlike humans, which use hemoglobin, which uses iron, which makes it red). Hemolymph or haemolymph is the Blood analogue used by all Arthropods and most Mollusks that have an Open circulatory system. Hemocyanins (also spelled haemocyanins) are respiratory Proteins in the form of Metalloproteins containing two Copper atoms that reversibly Copper (ˈkɒpɚ is a Chemical element with the symbol Cu (cuprum and Atomic number 29 The blood is propelled by a series of hearts into the body cavity where it comes in direct contact with the tissues. Arthropods are protostomes. Protostomia (from the Greek: mouth first) are a Taxon of Animals Together with the Deuterostomes and a few smaller phyla There is a coelom, but it is reduced to a tiny cavity around the reproductive and excretory organs, and the dominant body cavity is a haemocoel, filled with haemolymph, which bathes the organs directly. By the broadest definition a body cavity is any fluid filled space in a Multicellular organism. A hemocoel is a cavity or series of spaces between the organs of organisms with Open circulatory systems like most Arthropods and Mollusks A combination Hemolymph or haemolymph is the Blood analogue used by all Arthropods and most Mollusks that have an Open circulatory system. The arthropod body is divided into a series of distinct segments, plus a pre-segmental acron, which usually supports compound and simple eyes and a post-segmental telson. The telson is the last division of the body of a Crustacean. It is not considered a true segment because it does not arise in the embryo from teloblast areas These are grouped into distinct, specialised body regions called tagmata. Each segment, at least primitively, supports a pair of appendages. An appendage in the broadest sense is an additional or subsidiary part existing on or added to something which can generally still function if the appendage has never existed or
The cuticle in arthropods forms a rigid exoskeleton, composed mainly of chitin, which is periodically shed as the animal grows. An exoskeleton is an external Skeleton that supports and protects an animal's body in contrast to the internal Endoskeleton of for example a Human. Chitin ( C 8 H 13 O 5 N)n (ˈkaɪtən is a long-chain Polymer of a N-acetylglucosamine They contain an inner zone (procuticle), which is made of protein and chitin and is responsible for the strength of the exoskeleton. The procuticle is the major portion of the Exoskeleton of an Insect (and various other Arthropods; its exact composition and structure may differ somewhat The outer zone (epicuticle) lies on the surface of the procuticle. The epicuticle is the outermost portion of the Exoskeleton of an Insect (and various other Arthropods; its exact composition and structure may differ somewhat It is nonchitinous and is a complex of proteins and lipids. Proteins are large Organic compounds made of Amino acids arranged in a linear chain and joined together by Peptide bonds between the Carboxyl Lipids are broadly defined as any fat- Soluble ( lipophilic) naturally-occurring Molecule, such as fats oils waxes cholesterol sterols fat-soluble It provides the moisture proofing and protection to the procuticle. The exoskeleton takes the form of plates called sclerites on the segments, plus rings on the appendages that divide them into segments separated by joints. A sclerite ( Greek skleros meaning " hard " is a hardened body part This is in fact what gives arthropods their name — jointed feet — and separates them from their relatives, the Onychophora and Tardigrada, also called Lobopoda (and which is sometimes included in a group called Panarthropoda that also includes arthropods). The velvet worms ( Onychophora — literally "claw bearers" form a Clade within the Ecdysozoa and can be simply described as " Worms Tardigrades (commonly known as water bears) form the Phylum Tardigrada, part of the superphylum Ecdysozoa. Panarthropoda is a Taxon combining the phyla Arthropoda, Tardigrada and Onychophora. The exoskeletons of arthropods strengthen them against attack by predators and are impermeable to water. In order to grow, an arthropod must shed its old exoskeleton and secrete a new one. This process, ecdysis, is expensive in terms of energy, and during the molting period, an arthropod is vulnerable. Ecdysis is the Molting of the Cuticula in Arthropods and related groups ( Ecdysozoa)
Aside from these major groups, there are also a number of fossil forms — mostly from the lower Cambrian — including anomalocarids, euthycarcinoids and Arthrogyrinus, which are difficult to place, either from lack of obvious affinity to any of the main groups or from clear affinity to several of them. The Cambrian is a geologic period and system that began about Ma (million years ago at the end of the Proterozoic eon and ended about Ma with Anomalocaridids are a group of very early marine animals known from fossils found in Cambrian deposits in China, USA, Canada, Poland
The phylogeny of the arthropods has been an area of considerable interest and dispute. The validity of many of the arthropod groups suggested by earlier authors is being questioned by recent studies; these include Mandibulata, Uniramia and Atelocerata. In arthropods the mandible is either of a pair of Arthropod Mouthparts used for biting cutting and holding food S M Manton's (1973 polyphyletic Arthropod hypothesis with Uniramia as one of three Phyla The Atelocerata (Heymons 1901 is an obsolete Monophyletic group formed by the Hexapoda + Myriapoda, and sister group of the Eucrustacea, if The most recent studies tend to suggest a paraphyletic Crustacea with different hexapod groups nested within it. In Phylogenetics, a group of organisms is said to be paraphyletic if the group contains its most recent common ancestor but does not contain all  The remaining clade of Myriapoda and Chelicerata is referred to as Paradoxopoda or Myriochelata. The Myriochelata is a Clade consisting of the Myriapoda ( millipedes, and centipedes) and Chelicerata ( spiders and
Since the International Code of Zoological Nomenclature recognises no priority above the rank of family, many of the higher groups can be referred to by a variety of different names. The International Code of Zoological Nomenclature is a set of rules in Zoology that have one fundamental aim to provide the maximum universality and continuity in the naming 
Arthropods are today almost universally considered to be monophyletic, i. A clade is a taxonomic group comprising a single Common ancestor and all the descendants of that ancestor e. they only arose once, a view supported by both morphological and molecular studies. Such a view contradicts the widespread view in the 1970s that the arthropods had evolved on several occasions from soft-bodied, annelid-like ancestors.
The closest relatives of the arthropods are usually considered to be the Tardigrada and Onychophora, together forming the monophyletic group Panarthropoda (the crustaceans, myriapods, chelicerates and insects are often referred to as "Euarthropoda" to distinguish them from their soft-bodied relatives). Tardigrades (commonly known as water bears) form the Phylum Tardigrada, part of the superphylum Ecdysozoa. The velvet worms ( Onychophora — literally "claw bearers" form a Clade within the Ecdysozoa and can be simply described as " Worms Panarthropoda is a Taxon combining the phyla Arthropoda, Tardigrada and Onychophora. Euarthropod, or formally the Euarthropoda is a term that is often used to refer to the well-sclerotised arthropod clades i Comparison between these groups suggests that the euarthropods evolved from a soft-bodied ancestor not too dissimilar to the living onychophorans, a view that has found some support from the fossil record.
Traditionally the Annelida have been considered the closest relatives of these three phyla, on account of their common segmentation. The annelids, collectively called Annelida (from Latin anellus "little ring" are a large phylum of Animals comprising Molecular data however, is strongly against this grouping (known as the Articulata), suggesting instead that the panarthropods belong in a clade including both the arthropods and various pseudocoelomates such as roundworms and priapulids that share with them growth by moulting, or ecdysis, from which its name, the Ecdysozoa. A clade is a taxonomic group comprising a single Common ancestor and all the descendants of that ancestor By the broadest definition a body cavity is any fluid filled space in a Multicellular organism. The nematodes or roundworms ( Phylum Nematoda from Greek (nema "thread" + -ode "like" are one of the most common Priapulida ( priapulid worms or penis worms, from Gr πριάπος priāpos ' Priapus ' + Lat Ecdysis is the Molting of the Cuticula in Arthropods and related groups ( Ecdysozoa) The Ecdysozoa (ˌɛkdɪsəˈzoʊə are a grouping of Protostome animals including the Arthropoda ( Insects, Chelicerata, Crustaceans is derived. If this new grouping is correct, then segmentation of arthropods and annelids has either evolved through convergence, or has been inherited from a very deep ancestor, and has been subsequently lost in several other lineages, such as the non-arthropod members of the Ecdysozoa. Convergent evolution describes the acquisition of the same biological trait in unrelated lineages